My take on this concept is that when a horse is first started, having a job to do can assist a horse to get comfortable with just carrying a rider and following some direction.
WHAT IS A JOB?
When To Stop Giving A Horse A Job
For me, I can see the advantages in a young horse having a job to help it adapt to life as a riding horse. However, there comes a time when to continue with working at a job becomes a hindrance. At some point, the focus of the job needs to move from performing a set of routine tasks to being connected to the rider. It should never be that we tell a horse to do something and then wait until it’s done before telling it to do something else.